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‘Inside Out’ Façade Speeds Research Center Expansion
Skeptics suggested that the plan for expanding the Interdisciplinary Research Center at the Medical College of Georgia in Augusta was folly. There was no way that creating and installing precast concrete panels as a skin over a high-tech waterproofing membrane closer to the building interior would work, they suggested. Undaunted by the naysayers, the design team not only proceeded with their plans for the $22-million facility, but they made it work — and finished ahead of schedule.

“We were presented with some unique issues,” says architect Howard Wertheimer, principal with Lord, Aeck & Sargent Architecture in Atlanta. “This kind of laboratory presents an interesting challenge. The nature of the structure is such that it requires a controlled environment and tight building envelope to prevent contaminants of the research inside.” Negative-pressure zones in the laboratory areas can create a higher thermal/moisture drive through the exterior walls, Wertheimer explains.

As a core component of the college’s research campus, the facility had to provide space for several specialized research areas. These included such highly sensitive uses as an animal housing facility, tissue- and bacterial-culture suites, clean rooms, dark rooms and radio-isotope suites. These controlled environments must prevent contaminants from leaving or entering the research laboratories.

The need to finish the building within a limited time frame precluded the use of a typical precast cladding system. The solution was to create a “high-performance” barrier for the exterior envelope that was installed behind the precast exterior wall. That design allowed the precast concrete panels to be removed from the critical path for the envelope construction. Using precast as a veneer not only allowed it to meet the need better, it could be installed faster. Thus, the twin goals of high performance and a fast-track schedule were met with a precast concrete exterior that blended well with other structures on the medical school campus.

This unique solution allowed the building envelope to be installed first, with the precast exterior added afterward. That approach satisfied two objectives — providing schedule efficiency and cost effectiveness within the high-performance environment of a laboratory facility.

Precast Blended With Neighbors
The precast concrete exterior also met another criterion — the need to complement existing campus architecture, which ranges from brick and stucco to metal paneling. One inspiration for the exterior design came from a public library designed by renowned architect Marcel Breuer. This required great attention to detail, which included choosing an aggregate that allowed for the desired ribbing in the panel. This buff-colored, vertical ribbing created a building that, as Wertheimer says, “changes color even as the light changes. We wanted it to not be monochromatic but to be neutral and to reflect the style of the buildings surrounding it.”

To accomplish the design team’s goals, the precast panels feature a 3/8-inch-ribbed design with a light sandblast finish. The precaster, Metromont Prestress Co. in Greenville, S.C., worked backward from this requirement to choose an appropriate aggregate that provided a smooth edge on the panels. To determine that the finished panels would meet the design requirements, the design team reviewed an initial 1- by 1-foot panel. Then a 4- by 4-foot panel was prepared and presented to administrators for their approval. Eventually, a full-bay mockup was built at the precast plant.

Meetings between the architect, manufacturer and the contractor, Turner Construction Co. in Atlanta, established requirements for the concrete forms, aggregate, mix, sequencing and storage of the panels. A major concern during these meetings, according to Wertheimer, was to establish redundancy and repetition in the manufacture of the panels, to ensure the most cost-effective production. The panels’ installation was managed through a series of preconstruction meetings with the contractor, fabricator and architect. This included everything from the sequencing of construction to the shipping and placement of the panels.

A major challenge involved finding a way to protect the high-performance barrier during the installation of the precast pommels. Typical welding procedures would damage the critical material, thereby rendering it ineffective. The result was to create a unique plan to stack the exterior panels vertically and to weld only the bottom row of concrete panels. As additional panels were installed, they were attached to the panels below with mechanical fasteners. That design placed most of the weight load on the bottom row.

Interlocking Design
This decision required a unique design for the individual panels. So an interlocking “male-female” connection was created within the panel design. The precast panels alternated between and inverted “T” shape and an “I” shape so they would lock together, much like a set of children’s blocks. This decision resulted in two additional benefits. First, it created a stronger veneer. At the same time, the easily recognizable “lightning bolt” pattern created by the interlock provided strong visual clues that facilitated installation of the panels.

Connections, located in the cavity between the performance skin and the panels, were accessible only from the panels’ exteriors, requiring a method to allow installers to reach behind the panels to fasten the connections. The solution was provided by adding clear space behind the panels, making this space twice the “typical” size — four inches instead of two inches. To ensure the erectors could work within those confines, the designers conducted in-house studies and rough mock-ups of the clear space.

“The entire process hinged on the waterproofing membrane, which was installed and tested before the precast panels were erected,” says Wertheimer. “We didn’t want to rely on waterproofing the joints between the precast panels to maintain integrity in the envelope.”

That decision presented some unique challenges in the manufacture of the panels, according to George Spence, Metromont’s regional manager in Greenville. “It’s not unlike assembling a giant jigsaw puzzle,” he notes. “We were required to cast the panels to extremely tight tolerances in order to make the pieces fit together. It required a great deal of detailed form work and a level of precision over and above the tolerances normally demanded” by standards of the Precast/Prestressed Concrete Institute.

The problem was two-fold, he explains. “First, we had to pay greater attention to detail in the plant. It also required greater attention to layout in the field for the erection team. The process was unforgiving. If one piece was out of line, it would affect the entire process.”

Unique Erection Process
The erection process was unique as well. Since it was necessary to ensure the integrity of the waterproofing skin, the panels could not be fastened back into the cast-in-place structural frame of the building, as that would require penetrating the membrane. Instead, the panels rely on themselves for structural integrity. They are stacked on a series of precast concrete capitals at the bottom and tied together by welding only at the point of the lowest panels. From there, the panels were stacked and attached with mechanical fasteners, thereby transferring most of the load to the bottom row of panels. All connections to tie the outer skin back into the structure were located between the performance skin and the panels.

The system created a number of benefits, Wertheimer says. “We were able to cut approximately four weeks from the construction schedule,” he notes. Three weeks were saved by removing the fabrication of the concrete panels from the critical path and allowing them to be installed as a veneer. An additional week was saved in the fabrication and installation of the panels.

“Architecturally, the building only required a few simple shapes,” Wertheimer says. That allowed the erector to install the panels quickly from a small staging area, taking the panels straight from the trucks and erecting them. The panels arrived at night and were installed the next day. Because the plant is less than 300 miles from the construction site, shipping costs were relatively low. Also, the precast panels were small enough to be shipped under standard requirements, eliminating the need for additional transport fees.

Wertheimer also pointed to the repetition of the design as an advantage. “This minimized the need for a large number of special pieces. The precaster was able to use the same forms over and over.”

Although the project was unique, both Wertheimer and Spence agreed that the system had proven itself viable for future projects. “It was more costly than a simpler system would be,” notes Spence. “But, if the circumstances and needs were similar in another building, we proved that the system does work and would be appropriate.”